Water for human consumption originates from wells or lakes, and it is often desirable to filter the water before it is consumed, or used to process foods which may be contaminated thereby.
Although filters may exist in any number of configurations, filters usable by the general public to filter water within a home typically have a cylindrical chamber for receiving a replaceable tubular filter cartridge. The filter cartridge has an inner core or bobbin made of a suitable material such as polypropylene, which is inert, and will not cause contamination to the water being filtered. One commonly sized filter receives a filter cartridge having a perforated inner core with a diameter of approximately one inch and an overall length of approximately 10 inches.
Extending around the circumference of the inner core is a filter media, which may be made of any suitable substance, which has a fine porosity for providing a desired filtration. Specifically, the filter media must have porosity with openings therein sized to trap particles of contaminants within the filter media, and yet have pores sufficiently large to allow the water to pass there through. Although numerous filter media are currently available, a common media in filter cartridges employed for home use consist of polypropylene yarn wound around the core. Polypropylene is considered desirable because it is an inert material the presence of which will not cause contamination to the water being filtered. As an alternative to yarn or roving, a filter media has been made by blowing pieces of polypropylene fiber into a mat which is then wrapped around the filter core as shown in U.S. Pat. No. 4,048,075.
There are certain problems, however, with existing filter cartridges which employ polypropylene as a filter media. First, media made from polypropylene yarn, or roving, are manufactured to have properties similar to those of yarns made of natural fibers, such as cotton yarn. Such synthetic yarns, therefore, have lubricants and other chemicals on their surfaces to reduce friction between adjacent fibers and anti-static agents to control the effects of static electricity. In the absence of an anti-static agent, static electricity will build up on the fibers and cause the fibers to repel one another such that they cannot be spun into yarn. When synthetic yarn having chemicals on the surfaces thereof are used as a filter media, some of the chemicals will become dissolved in the water being filtered, thereby causing a degree of contamination to the filtered water.
Although it is theoretically possible to wash the lubricants and other chemical material out of the manufactured filters, such rinsing would be time consuming and expensive. Once washed, the filters must be dried prior to packaging, and the drying process would require the application of heat for a duration of time which would greatly enhance the cost of the end product.
Bruckner, U.S. Pat. No. 4,933,130 discloses a method of manufacturing a spin finish free yarn for a polymer having a glass transition above 100 centigrade. This method employs a drawing step to evaporate liquid used to avoid static. Ploypropylene, however, has a glass transition of −15 Centigrade.
Another problem with existing filter media made from polypropylene is that the filaments thereof are not continuous. During the course of manufacture of the yarn, filaments of polypropylene are cut into lengths ranging from one inch to four inches long. Similarly, filter media formed as a mat wrapped around a core are also made from relatively short lengths of filament. When existing polypropylene filter media are used to filter water, small fragments of polypropylene fibers are subject to “migration” within the filter mass. Specifically, some of the fragments of the fibers may escape the mass of the filter media and enter the stream of otherwise filtered water such that the filter itself again causes some contamination to the water.
Despite the problems which have existed with its use, polypropylene stands as a leading choice for a filter media. It would, therefore, be desirable to provide a filter media which employs polypropylene fibers but which would not be subject to the migration of filament fragments into the water stream and would not have surface chemicals which could contaminate the water being filtered.